The National Heart Forum analysed obesity studies from the mid-70s until 2007 and found that obesity among the young is levelling off. Forecasts for 2020 predict the number of overweight boys aged 2 to 11 will fall from 22% today to 17%, and girls from 34% to 17%.
NHF chairman and Oxford professor Klim McPherson, who authored the report, said the figures were still "unacceptably high" but credited greater awareness of the problem for the fall.
McPherson said it was difficult to pinpoint a single reason for the increase in obesity but said the restrictions on advertising to children and food labelling had been successful in halting its rise. However he still believes marketers and regulators need to do more.
He said brands should be using the "traffic light" food labelling system indicating the amount of fat, salt and sugar in products, rather than guideline daily amounts.
McPherson said he would like to see more restrictions for when "toxic food" can be advertised and added that junk food brands should be stopped from advertising on programmes between 6pm and 9pm.
McPherson said: "I would like to see an end to the marketing of toxic products and to marketing junk food on programmes children watch as opposed to children’s programmes.
"You don't show cigarette advertising at that time so I don't see the point of advertising junk food that has no nutritional value and just makes you fat."
The predictions are also positive for young adults aged between 12 and 19. The number of overweight and obese boys will decrease from 25% to 18% and 19% to 6% respectively. The same figures for girls are 35% to 29% and 30% to 9%.
McPherson said: "These trends present a more positive picture that obesity may be levelling off in children. However, prevalence, and current trends, of excess weight are still unacceptably high and these figures should not be taken as an argument for complacency.
"The government needs to keep up the work they are doing to tackle obesity."